Openvpn from Debian 10 to 11, stop to routing all my packets

Solution 1:

Solution found. On Debian 11 they had a bad(imho) idea to rename the classical eth0 to a long name of 16 char! This make impossible the use of interface in iptables or bridgge-utils(the maximum network interface lenght allowed is 15) otherwise will get this error "interface name is longer than 15 characters" So my nat goes to a non existent device(the eth0 disappeared). But fortunately there is an easy solution:

vim /etc/udev/rules.d/70-persistent-net.rules

#/etc/udev/rules.d/70-persistent-net.rules
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="YO:UR:MA:CA:DD:RES", ATTR{type}=="1", KERNEL=="eth*", NAME="eth0"

Of course replace "YO:UR:MA:CA:DD:RES"

After a reboot, i see the old good eth0 name and all return to work